1. Field of the Invention
The present invention relates to therapeutically active azabicyclic compounds, a method of preparing the same and to pharmaceutical compositions comprising the compounds.
The novel compounds are useful as stimulants of the cognitive function of the forebrain and hippocampus of mammals and especially in the treatment of Alzheimer's disease.
2. Description of Related Art
Due to the in general improved health situation in the western world, elderly-related diseases are much more common now than in the past and are likely to be even more common in the future.
One of the elderly-related symptoms is a reduction of the cognitive functions. This symptom is especially pronounced in the pathophysiological disease known as Alzheimer's disease. This disease is combined with, and also most likely caused by, a up to 90% degeneration of the muscarinic cholinergic neurons in nucleus basalis, which is part of substantia innominata. These neurons project to the prefrontal cortex and hippocampus and have a general stimulatory effect on the cognitive functions of the forebrain as well as of hippocampus, namely learning, association, consolidation and recognition.
It is a characteristic of Alzheimer's disease that although the cholinergic neurons degenerate, then the postsynaptic muscarinic receptors in the forebrain and hippocampus still exist. Therefore muscarinic cholinergic agonists are useful in the treatment of Alzheimer's disease and in improving the cognitive functions of elderly people.
It is well known that arecoline (methyl 1-methyl-l,2,5,6-tetrahydropyridine-3-carboxylate) is such a cholinergic agonist.
Arecoline however has a very short biological half life and a small separation between central and peripheral muscarinic effects. Furthermore arecoline is a rather toxic compound.
EP-A-0307142 discloses a class of thiadiazoles, substituted on one of the ring carbon atoms with a non-aromatic azacyclic or azabicyclic ring system, and substituted on the other ring carbon atom with a substituent of low lipophilicity, or a hydrocarbon substituent, which are muscarinic agonists and therefore useful in the treatment of neurological and mental illnesses and severe painful conditions.
It is an object of the invention to provide new muscarinic cholinergic compounds.